It is often desirable to uniquely label or identify items, such as large or small objects, plants, and/or animals for sorting, tracking, identification, verification, authentication, or for other purposes. For example, in a form of chemical synthesis in combinatorial chemistry known as “solid phase” chemical synthesis, encoded beads or particles are used as a solid support for the synthesis of chemicals and or chemical libraries. The encoded beads or particles are used identify the attached chemicals.
In another example, in a DNA/genomic sequencing assay commonly referred to as a “random bead assay”, known DNA sequences (probes) are attached to encoded beads or particles. The beads are then mixed with a labeled target analyte, and segments of the DNA sequence of the labeled target analyte will selectively bind to complementary DNA segments of the probe. The known probes are then spatially separated and examined for fluorescence. The beads that fluoresce indicate that the DNA sequence strands of the target analyte have attached or hybridized to the complementary DNA on that bead. The DNA sequences in the target analyte can then be determined by identifying the code on the bead, which uniquely identifies the complementary DNA (or cDNA) sequence of each probe. In addition the level of fluorescence is indicative of how many of the target molecules hybridized to the probe molecules for a given bead.
Existing technologies for uniquely labeling or identifying items, such as bar codes, electronic microchips/transponders, radio-frequency identification (RFID), and fluorescence (or other optical techniques), are often inadequate. For example, existing technologies may be too large for certain applications, may not provide enough different codes, may require specific alignment of particles to the detector, or cannot withstand harsh environments, e.g., harsh temperature, pressure, chemical, nuclear and/or electromagnetic environments.
Therefore, it would be desirable to obtain a labeling technique that provides the capability of providing many codes (e.g., greater than 1 million codes), that can be made very small, that can withstand harsh environments, and/or be independent of orientation with respect to the detector.